1. Field of the Invention
The present invention pertains generally to a method of labeling containers in which a stationary vacuum plate assembly provides different levels of vacuum to a rotating vacuum drum used to support segments of label material, and more particularly to a vacuum drum with a floating shoe to provide improved control over label segments during processing.
2. Description of the Background Art
Labeling containers by applying preprinted film labels is a popular alternative to conventional lithography. Various environmental problems, including air pollution and recycling concerns, strongly favor adoption of preprinted films for labeling containers. Plastic containers, metal cans and glass bottles can be labeled effectively with film labels.
Cost considerations have led to the development of thin films which have the advantage of reducing the cost of materials used, but require increasingly more stringent process controls to allow high speed labeling equipment to handle thin, stretchable, and relatively flimsy labeling materials.
Labeling speed is an important consideration in high production canning and bottling plants, since it is unacceptable for labeling processes to impede productivity of a bottling or canning line. Labeling speed is of paramount importance, with labeling speeds in excess of ten containers per second being possible to achieve with some labeling materials. Generally, thicker materials that are resistant to stretching are easier to handle by conventional labeling machines.
When thin labeling materials are run at high speeds, problems, such as label splitting, stretching labels and misalignment of labels, are encountered. With roll-fed labels, when the labels are cut from the web of label material, excessive tension on the label can cause the labels to split instead of being cut. Similarly, over-tensioning thin labels can cause the labels to stretch as they are applied to the vacuum drum. As the labels are transferred to a vacuum drum, excessive vacuum can cause the label segment to shift or snap, leading to misaligned labels on the containers.
Some labeling materials include coatings or treatments that result in higher coefficients of friction that can interfere with the labeling process. Labels having a higher coefficient of friction tend to become over-tensioned more easily, which aggravates problems associated with over-tensioning.
Another problem encountered when labels are supported by a vacuum drum during the labeling process is that glue applicators for applying glue to the label segments can become jammed by labels if insufficient vacuum is provided to prevent the labels from following the glue applicator.
Therefore, there is a need for a method of selectively controlling the amount of vacuum supplied to a vacuum drum during different stages of the labeling process. The present invention satisfies that need, as well as others, and overcomes deficiencies found in current label handling techniques.
The present invention pertains to a multiple-port valve plate assembly for use with a rotating vacuum drum in a label apparatus of the type described in U.S. Pat. No. 5,486,253, which is incorporated herein by reference. By way of example, and not of limitation, the apparatus generally comprises a disk-shaped valve body, having first and second arcuate-shaped stationary vacuum cavities, and a floating shoe positioned in a receptacle in the valve body intermediate to the position of the first and second stationary vacuum cavities. The floating shoe, which moves within the receptacle, has a third arcuate-shaped vacuum cavity that also moves, or xe2x80x9cfloatsxe2x80x9d, in the valve body with the floating shoe. A spring material, such as sponge rubber, is positioned between the floating shoe and the inner wall of the receptacle so as to hold the floating shoe against the wear plate in the system. One of the stationary vacuum cavities is divided into two spaced-apart arcuate-shaped segments that are interconnected by a channel in the valve body, and a vacuum control valve is provided for controlling the amount of vacuum supplied by the interconnecting channel to one of the segments. In addition, a pressure port for blow-off is also provided in the valve body. Each of the stationary vacuum cavities and the floating shoe include vacuum fittings configured for coupling the cavities to separate sources of vacuum.
The first stationary vacuum cavity is configured to be supplied with a level of vacuum suitable for the vacuum drum picking up a label segment from a cutter with limited tension. The intermediate floating cavity is configured to be supplied with another, higher level of vacuum suitable for the vacuum drum firmly griping the cut label segment as an adhesive is applied to the label segment. The second stationary vacuum cavity is configured to be supplied with a lower level of vacuum suitable for the vacuum drum holding the label while the label is being transferred to a container. The pressure port is configured to be provided with a high pressure for facilitating release of the label from the vacuum drum as it contacts the container.
The present invention improves the seal between the fixed valve plate and the rotating vacuum drum at the point of high vacuum so that vacuum loss is reduced. This reduced vacuum loss has the advantage of allowing a smaller vacuum source to be used to maintain the high vacuum level, thus reducing the cost of the vacuum pump or generator, thereby reducing the operational cost to produce the vacuum. It also provides a more precise control of the vacuum at the point of adhesive application and eliminates the spread of high vacuum to adjacent ports that can negatively affect the label cutting and application by changing the vacuum level in these adjacent ports and chambers on a random basis. On a standard valve plate, the vacuum seal can be affected by warping and/or wear of the plate caused by heat and general use. The floating shoe reduces the effect of warping or wear by reducing the contact surface area at the critical high vacuum point. It also reduces the amount of heat generated because the force between the valve plate and the vacuum drum required to maintain a good vacuum seal is concentrated over a small surface area. By reducing the heat, the potential for warping and general wear of the valve plate is reduced, which is particularly important during high speed labeling.
An object of the invention is to provide a vacuum plate assembly with a plurality of cavities for providing different levels of vacuum to a vacuum drum in a container labeling apparatus, wherein thin films can be swiftly and accurately applied with minimum scrap or wastage.
Another object of the invention is to provide a vacuum plate assembly with a plurality of cavities for providing different levels of vacuum to a vacuum drum in a container labeling apparatus, wherein ultra-thin stretchable film can be applied without reducing labeling speeds or over-tensioning label material during the labeling process.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.